1. Field of the Invention
This invention relates to a methacrylic resin composition with improved tacky adhesion and to a method for the preparation thereof, and more particularly to an improved adherent methacrylic resin composition to obtain cross-linked molded articles such as molded products, laminated moldings and coated materials, and to an improved method for the preparation thereof.
2. Description of the Prior Art
Generally, methacrylic resins formed predominantly of methyl methacrylate have found use in covers of lamps, parts for automobiles, sign-boards, ornamental articles, sundry goods etc. because of their excellent weatherability and outstanding transparency. Since the aforementioned methacrylic resins are linear polymers, they have some disadvantages that they are deficient in resistance to heat, to solvents, to shock and to surface hardness.
For example, the methacrylic resins are heat resistant up to about 100.degree. C. at most so that they are inadequate at present to meet specific requirements in various applications demanding higher temperature resistances.
In the case of parts for automobiles, the methacrylic resins can not be used for head lamp covers because of their inadequate heat resistances. In the case of tail lamps, since the amount of heat generation has been increasing due to the increase in lamp size and illumination and the shifting to smaller thickness of the lamp covers required for cost cut, the necessity of improving heat resistance of the lamp covers is becoming more marked.
The methacrylic resins are expected to find growing applications in parts such as covers for meters on automobiles and two-wheelers and covers for water heaters using solar thermal energy which by nature experience great elevation of temperature under direct exposure to the sunlight. Thus, the development of a methacrylic resin resistant to higher temperatures than the boiling point of water is longed for.
For the purpose of conferring an improved heat resistance to a methacrylic resin, there have been proposed various methods. Recently, U.S. Pat. No. 4,791,184 discloses a methacrylic resin molding material comprising a partially cross-linked polymer gel which is apt to do moldings required to flow such as injection moldings, extrusion moldings and transfer moldings. The methacrylic resin molding material can give cross-linked molded articles with excellent resistances to heat, solvents etc. without degrading transparency.
Since the methacrylic resin molding material, however as described in the patent specification, is non-sticky and shape-retaining, in the case of kneading to improve fluid properties, a partially cross-linked polymer gel with a higher polymer content or a partially cross-linked polymer gel obtained by partially polymerizing by a mixture of monomers alone has the problem of being difficult to handle because it is in the form of loose separate fine particles. In the case of preforming into the corresponding shape of a complexed molding article or feeding of molding material into a complexed shaped mold, there is a problem that the retaining of preformed shape is difficult or the molding material feeding is complicated.
In the case of blending fillers such as inorganic powders comprising aluminum hydroxide, alumina, silica, talk, calcium carbonate etc., glass fibers and wood powders to the aforementioned molding materials, it is difficult to mix homogeneously because of the non-sticky characteristics of the molding materials. Especially, in the case of using mixed dispersively or kneaded partially cross-linked polymer gel obtained partially polymerizing a mixture of monomers alone, the molded products tend to have cracks because of the heterogeneous mixing occurred depending on the amount of blended fillers.
For the purpose of obtaining a laminated molding consisting of a methacrylic resin sheet adhered to the same methacrylic resin or other resin sheets, there have been used (a) a method using a volatile organic solvent capable of dissolving the resin (Japanese Patent Publication No. SHO 60(1985)-56177), (b) a method using an adhesive prepared by admixing a polymerizable material selected from the group consisting of methyl methacrylate monomer, a monomer mixture predominantly consisting of methyl methacrylate, and a partial polymer thereof, with an amine and an catalyst thereof (Japanese Patent Publication No. SHO 62(1987)-42951).
However, these methods have a problem such that the adhesive solutions tend to generate small bubbles on adhesive interfaces or in thick adhesive layers, to develop color in adhesive layers, and to smell strongly, and require special skills for the preparation and application of these adhesives.
Also these methods have a disadvantage that the adhesive solutions can not bond or can only weakly bond plastic materials resistant to solvents, especially cross-linked plastic materials because swelling or dissolving with the solutions of the bonding surface of the methacrylic resin to be bonded is the base for bonding by these methods.
In many applications, methacrylic resins have been coated on various different plastics and decorative materials for transparent and decorative surface finishing.
Conventionally various methods for coating have been proposed, e.g. (c) a method for preparing a coated product by impregnating a syrup consisting of methyl methacrylic monomer and linear polymer thereof, and pressuring and compressing (Japanese Patent Laid-open No. SHO 49(1974)-1,94804), (d) a method for preparing a coated product by laminating a methacrylic resin sheet on a decorative sheet by heating and pressing (Japanese Patent Laid-open No. SHO 47(1972)-11396), and (e) a method preparing a coated material by applying a methacrylic resin film on a surface of an uncured substance containing polymerizable monomers and solvents, and heating and polymerizing the uncured substance (Japanese Patent Laid-open SHO 57(1982)-135122).
However, the surface of the above-mentioned coated articles has insufficient resistance to heat and to solvents because the methacrylic resin constituting the coating is a linear polymer. Further, the method of impregnating a syrup (c) is superior in adhesion, but has difficulties to get a heavy thickness of coating and needs complicated processes. The method of using a methacrylic resin sheet (d) or film (e) can get a thick coating layer, but needs additional complicated processes to prepare the sheet or film previously and the products are deficient in adhesion in some cases.
An object of this invention, therefore, is to provide a novel methacrylic resin molding material having superior characteristics such as improved tacky adhesion, easy handling and homogeneous mixing of fillers, and a method for preparation thereof.
Another object of this invention is to provide an adhesive overcoming these disadvantages such as forming of small bubbles on adhesive interface, developing color, strong smelling, and requiring special skills, more particularly to provide an adhesive capable of bonding plastics resistant to solvents.
A further object of this invention is to provide a coating material having a good permeability and fluidity comparable to syrup, and easy-to-handle, more particularly to provide a coating material forming a coating layer resistant to heat and to solvents, having superior adhesion, and capable of easily control of coating thickness.